Products that must be heated after being packaged in order to sterilize their contents include disposable contact lenses and some food products such as meats. Disposable contact lenses are usually packaged in blister packages consisting of 2 pieces: a base and a lid. The base is an injection molded plastic shaped to include a bowl-shaped or rectangular recess for receiving the contact lens. Each blister pack generally contains a contact lens and enough solution to prevent drying and to maintain the contact lens ready for use.
The lid covering the base is heat sealed over the recess containing the contact lens. Then the package is retorted in an autoclave to sterilize the contents. A lidstock material for the lid must possess sufficient burst strength during and after autoclaving to keep the package sealed so that contact lens solution does not escape throughout the shelf life of the blister pack. The lid must also be peelable from the base in order to provide easy access to the contact lens held within the blister pack.
Lidstock materials suitable for covering openings in packages for contact lenses and foods are known in the prior art. However, the prior art lidstock materials generally suffer from one or more serious disadvantages making them less than entirely suitable for their intended purpose.
A principal objective of the present invention is to provide a lidstock material for lids requiring improved burst strength.
A related objective of the invention is to provide a lidstock material for making heat sealable and peelable lids on plastic containers.
Additional objectives and advantages of the present invention will become apparent from the following detailed description of some preferred embodiments.